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4d001e96 MD |
1 | #ifndef _URCU_WFQUEUE_STATIC_H |
2 | #define _URCU_WFQUEUE_STATIC_H | |
3 | ||
4 | /* | |
5 | * wfqueue-static.h | |
6 | * | |
7 | * Userspace RCU library - Queue with Wait-Free Enqueue/Blocking Dequeue | |
8 | * | |
9 | * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See wfqueue.h for linking | |
10 | * dynamically with the userspace rcu library. | |
11 | * | |
12 | * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
13 | * | |
14 | * This library is free software; you can redistribute it and/or | |
15 | * modify it under the terms of the GNU Lesser General Public | |
16 | * License as published by the Free Software Foundation; either | |
17 | * version 2.1 of the License, or (at your option) any later version. | |
18 | * | |
19 | * This library is distributed in the hope that it will be useful, | |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
22 | * Lesser General Public License for more details. | |
23 | * | |
24 | * You should have received a copy of the GNU Lesser General Public | |
25 | * License along with this library; if not, write to the Free Software | |
26 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
27 | */ | |
28 | ||
29 | #include <pthread.h> | |
30 | #include <assert.h> | |
b57aee66 | 31 | #include <poll.h> |
4d001e96 MD |
32 | #include <urcu/compiler.h> |
33 | #include <urcu/uatomic_arch.h> | |
34 | ||
35 | #ifdef __cplusplus | |
36 | extern "C" { | |
37 | #endif | |
38 | ||
39 | /* | |
40 | * Queue with wait-free enqueue/blocking dequeue. | |
41 | * This implementation adds a dummy head node when the queue is empty to ensure | |
42 | * we can always update the queue locklessly. | |
43 | * | |
44 | * Inspired from half-wait-free/half-blocking queue implementation done by | |
45 | * Paul E. McKenney. | |
46 | */ | |
47 | ||
48 | #define WFQ_ADAPT_ATTEMPTS 10 /* Retry if being set */ | |
49 | #define WFQ_WAIT 10 /* Wait 10 ms if being set */ | |
50 | ||
b57aee66 | 51 | static inline void _cds_wfq_node_init(struct cds_wfq_node *node) |
4d001e96 MD |
52 | { |
53 | node->next = NULL; | |
54 | } | |
55 | ||
b57aee66 | 56 | static inline void _cds_wfq_init(struct cds_wfq_queue *q) |
4d001e96 MD |
57 | { |
58 | int ret; | |
59 | ||
16aa9ee8 | 60 | _cds_wfq_node_init(&q->dummy); |
4d001e96 MD |
61 | /* Set queue head and tail */ |
62 | q->head = &q->dummy; | |
63 | q->tail = &q->dummy.next; | |
64 | ret = pthread_mutex_init(&q->lock, NULL); | |
65 | assert(!ret); | |
66 | } | |
67 | ||
b57aee66 PM |
68 | static inline void _cds_wfq_enqueue(struct cds_wfq_queue *q, |
69 | struct cds_wfq_node *node) | |
4d001e96 | 70 | { |
16aa9ee8 | 71 | struct cds_wfq_node **old_tail; |
4d001e96 MD |
72 | |
73 | /* | |
74 | * uatomic_xchg() implicit memory barrier orders earlier stores to data | |
75 | * structure containing node and setting node->next to NULL before | |
76 | * publication. | |
77 | */ | |
78 | old_tail = uatomic_xchg(&q->tail, node); | |
79 | /* | |
80 | * At this point, dequeuers see a NULL old_tail->next, which indicates | |
81 | * that the queue is being appended to. The following store will append | |
82 | * "node" to the queue from a dequeuer perspective. | |
83 | */ | |
6cf3827c | 84 | CMM_STORE_SHARED(*old_tail, node); |
4d001e96 MD |
85 | } |
86 | ||
87 | /* | |
88 | * It is valid to reuse and free a dequeued node immediately. | |
89 | * | |
90 | * No need to go on a waitqueue here, as there is no possible state in which the | |
91 | * list could cause dequeue to busy-loop needlessly while waiting for another | |
92 | * thread to be scheduled. The queue appears empty until tail->next is set by | |
93 | * enqueue. | |
94 | */ | |
b57aee66 | 95 | static inline struct cds_wfq_node * |
16aa9ee8 | 96 | ___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q) |
4d001e96 | 97 | { |
16aa9ee8 | 98 | struct cds_wfq_node *node, *next; |
4d001e96 MD |
99 | int attempt = 0; |
100 | ||
101 | /* | |
102 | * Queue is empty if it only contains the dummy node. | |
103 | */ | |
6cf3827c | 104 | if (q->head == &q->dummy && CMM_LOAD_SHARED(q->tail) == &q->dummy.next) |
4d001e96 MD |
105 | return NULL; |
106 | node = q->head; | |
107 | ||
108 | /* | |
109 | * Adaptative busy-looping waiting for enqueuer to complete enqueue. | |
110 | */ | |
6cf3827c | 111 | while ((next = CMM_LOAD_SHARED(node->next)) == NULL) { |
4d001e96 MD |
112 | if (++attempt >= WFQ_ADAPT_ATTEMPTS) { |
113 | poll(NULL, 0, WFQ_WAIT); /* Wait for 10ms */ | |
114 | attempt = 0; | |
115 | } else | |
06f22bdb | 116 | caa_cpu_relax(); |
4d001e96 MD |
117 | } |
118 | /* | |
119 | * Move queue head forward. | |
120 | */ | |
121 | q->head = next; | |
122 | /* | |
123 | * Requeue dummy node if we just dequeued it. | |
124 | */ | |
125 | if (node == &q->dummy) { | |
16aa9ee8 DG |
126 | _cds_wfq_node_init(node); |
127 | _cds_wfq_enqueue(q, node); | |
128 | return ___cds_wfq_dequeue_blocking(q); | |
4d001e96 MD |
129 | } |
130 | return node; | |
131 | } | |
132 | ||
b57aee66 | 133 | static inline struct cds_wfq_node * |
16aa9ee8 | 134 | _cds_wfq_dequeue_blocking(struct cds_wfq_queue *q) |
4d001e96 | 135 | { |
16aa9ee8 | 136 | struct cds_wfq_node *retnode; |
4d001e96 MD |
137 | int ret; |
138 | ||
139 | ret = pthread_mutex_lock(&q->lock); | |
140 | assert(!ret); | |
16aa9ee8 | 141 | retnode = ___cds_wfq_dequeue_blocking(q); |
4d001e96 MD |
142 | ret = pthread_mutex_unlock(&q->lock); |
143 | assert(!ret); | |
144 | return retnode; | |
145 | } | |
146 | ||
147 | #ifdef __cplusplus | |
148 | } | |
149 | #endif | |
150 | ||
151 | #endif /* _URCU_WFQUEUE_STATIC_H */ |